1. Field of the Disclosure
The present application relates to a flexible organic electroluminescent device, and more particularly, to a flexible organic electroluminescent device and a fabrication method thereof to enhance a banding property.
2. Discussion of the Related Art
The organic electroluminescent device emits light by enabling excitons within an emission layer to transition from an excitation state to a ground (a base) state. The excitons are formed through recombination of electrons and holes which are injected from an electron injection electrode and a hole injection electrodes into the emission layer.
Such an organic electroluminescent device driven in the above-mentioned principle has a self-luminous property. Also, the organic electroluminescent device can reduce thickness and weight because of being unnecessary for a separated light source unlike a liquid crystal display device. Moreover, the organic electroluminescent device has high grade properties such as low consumption power, high brightness, fast response time, and so on. As such, the organic electroluminescent device is being considered as a next generation display device of mobile electrical appliances. Furthermore, the organic electroluminescent device can be fabricated through a simple fabrication procedure. In accordance therewith, the organic electroluminescent device can largely reduce fabrication cost compared to the liquid crystal display device.
Meanwhile, the display devices are required to have flexibility. As such, flexible display devices are being actively researched.
FIG. 1 is a cross-sectional view showing an ordinary flexible organic electroluminescent device. In detail, FIG. 1 is an enlarged cross-sectional view largely showing an organic light emitting diode E and a driving thin film transistor TD.
With reference to FIG. 1, the ordinary flexible organic electroluminescent device includes a switching thin film transistor (not shown) and a driving thin film transistor TD which are formed on a first substrate 100, a planarization film 121 covering the driving thin film transistor TD, and an organic light emitting diode E.
The switching thin film transistor and the driving thin film transistor TD can be formed in one of an edge stopper structure and a coplanar structure. Hereinafter, a driving thin film transistor TD of the coplanar structure will be explained.
The driving transistor TD with the coplanar structure includes: a buffer layer 101 formed on the entire surface of the substrate 100; an active layer 110 formed on the buffer layer 101; a gate insulation film 114 and a gate electrode 115 which are sequentially formed on the active layer 110; and an interlayer insulation film 116 and source and drain electrodes 119a and 119b which are sequentially formed on the gate electrode 115.
The active layer 110 is defined into a channel region 112 and source/drain regions 113 and 111 formed in both ends thereof. The source and drain electrodes 119a and 119b are connected to the source and drain regions 113 and 111 of the active layer 110.
The organic light emitting diode E includes: a first electrode 131 formed on the planarization film 121 opposite to a pixel; an organic emission layer 133 formed in a region of the first electrode which is defined by an organic bank film 132 covering edges of the first electrode 131; and a second electrode 134 formed on the organic emission layer 133.
A sealing layer 140 and a front film 150 are sequentially formed on the second electrode 134 of the organic light emitting diode E.
The active layer 110 can become a polysilicon film which is formed a low temperature polysilicon (LTPS) process. In this case, a hydrogenation process must be performed for the active layer 110. Such a hydrogenation process forces a silicon nitride (SiNx) layer to be formed in an upper or lower portion of the driving transistor TD. However, the silicon nitride (SiNx) layer is easy to crack. Due to this, the silicon nitride (SiNx) layer can cause cracks when a banding process is performed.